Green Synthesis Of Silver Nanoparticle Using Poria Cocos(Schw.)Wolf Polysaccharide And Its Application

Poria cocos(Schw.)Wolf polysaccharide(PCP)is the main functional active ingredient of Poria,accounting for about 70%~90% of the dry weight of Poria sclerotia,with good biocompatibility and medicinal properties,including antioxidant,antitumor,anti-inflammatory,etc.,and has a certain bacteriostatic effect,but the broad spectrum of bacteriostatic is poor;Nanotechnology is a new type of technology,silver nanoparticles(Ag NPs)due to its special structure and physical and chemical properties,has unique chemical stability,thermal stability and antibacterial activity,but nanosilver particle size distribution is wide,and easy to agglomerate,need to add stabilizers to prevent agglomeration.Therefore,this study intends to use Poria cocos(Schw.)Wolf polysaccharide as a reducing agent and stabilizer,and synthesize nano-silver particles "green" to explore the stabilizing effect of Poria cocos(Schw.)Wolf polysaccharide on nano-silver and its bacteriostatic ability,and to study its application in food packaging and food preservation.In this paper,the extraction process of Poria cocos(Schw.)Wolf polysaccharide was optimized in response to the surface method,and the structure of Poria cocos(Schw.)Wolf polysaccharide was identified by ultraviolet-visible spectroscopy,Fourier infrared spectroscopy,gel chromatography and high performance liquid chromatography.Then,the extracted Poria cocos(Schw.)Wolf polysaccharide was used as reducing agent and stabilizer and Ag NO3 to synthesize Ag NPs particles(PCP-Ag NPs)under ultraviolet irradiation,and their structural characterization was studied by ultraviolet spectroscopy,infrared spectroscopy,particle size potential analysis,X-ray diffraction(XRD),transmission electron microscopy(TEM)and scanning electron microscopy(SEM),and their antibacterial activity was studied by paper diffusion,determination of MIC and MBC and bacteriostatic kinetic experiments.Then,the obtained Ag NPs particles and chitosan were used to make Ag NPs/CS composite films,and the membrane properties were studied by infrared spectroscopy,thermogravimetric analysis(TG),differential scanning calorimetry(DSC)and scanning electron microscopy(SEM).Finally,the film solution was coated on strawberries and monitored during different storage periods to investigate its application characteristics in strawberry postharvest preservation.The main findings are as follows:(1)The optimal process for PCP extraction by xylanase enzymatic method,with polysaccharide extraction rate as the index,and the best process for PCP extraction by single factor and response surface optimization is: enzymatic hydrolysis p H is 3.6,enzymatic hydrolysis temperature is 59.5 °C,and the time is 159 min,under this condition,the PCP extraction rate is 7.14%.Then,the extracted PCP was deproteinized and dialyzed for structural identification.,and the total sugar content of PCP was 69.37%,which was a pyran-type polysaccharide containing β-type glycosidic bonds.PCP has a molecular weight of 3652.62 k Da,which is mainly composed of 7 monosaccharides: fucosse,rhamnose,galactose,glucose,mannose,galacturonic acid and glucuronic acid,and its molar ratio is0.34:5.07:0.86:11.56:0.50:0.75:2.03.Among them,glucose,rhamnose,glucuronic acid and galactose accounted for a relatively high proportion of four monosaccharides,accounting for 56.05%,24.86%,10.59% and 4.16%,respectively.(2)The reaction conditions of PCP-Ag NPs were Ag NO3 concentration of 6m M/L,reaction time was 24 h,and PCP concentration was 0.1 mg/m L;The resulting PCP-Ag NPs are spherical and have a face-centered cubic structure.The synthesized solution of Ag NPs has a characteristic absorption peak near λ=450 nm and is reddish-brown.The functional groups in PCP participated in the reduction and stabilization process of Ag NPs,and the average hydrated particle size of the prepared PCP-Ag NPs was about 44.45±0.62 nm,which was normally distributed,and the Zeta potential was-40.8 m V,which was well stable.(3)The diameter of the inhibitory circle of PCP-Ag NPs against Staphylococcus aureus,Escherichia coli and Pseudomonas aeruginosa was 10.36±1.07 mm,11.14±0.79 mm and 10.39±0.14 mm,respectively,by paper diffusion,while 0.1mg/m L PCP did not show bacteriostatic activity against the three test bacteria;The minimum inhibitory concentration(MIC)and minimum bactericidal concentration(MBC)of Ag NPs against Staphylococcus aureus were 6.25 μg/m L and 12.5 μg/m L,respectively,MIC and MBC were 6.25 μg/m L for Escherichia coli,and MIC and MBC were 6.25 μg/m L and 12.5 μg/m L for Pseudomonas aeruginosa,respectively.(4)According to the appearance color of the film and the infrared spectroscopy results,Ag NPs were successfully incorporated into the chitosan(CS)substrate,and the addition of Ag NPs reduced the elongation at break and light transmittance of the CS film,and at the same time improved the internal structure of the CS film to make it more compact.In addition,the addition of Ag NPs can also improve the thermal stability of CS films.(5)By monitoring the appearance and nutrient changes of strawberries at different storage periods,it was found that the addition of Ag NPs could improve the preservation effect of CS film on strawberries.Compared with the blank group and CS coating group,the spoilage rate of strawberries treated with PCP-Ag NPs/CS coating film was significantly reduced,and PCP-Ag NPs/CS coating film could delay the changes of hardness,soluble solids,p H and titratable acid equivalent values of strawberries during storage,and maintain the appearance quality to a certain extent.The results of this paper aim to provide a theoretical basis and application technical support for Ag NPs as food antibacterial agents and preservatives.